Vinyl esters of carboxylic acids and their production



Patented Dec. 29, 1936 PATENT OFFICE v VINYL ESTERS OF CARBOXYLIC ACIDS AND THEIR PRODUCTION Walter Reppe, Ludwigshafen-on-the-Rhine, Germany, assignor to I. G. Farbenindustrie Aktiengesellschaft; Frankfort-on-the-Main, Germany I No Drawing. Application January 4, 1933, Serial No. 650,145. In Germany March 5, 1932 11 Claims. (01. 260106) The present invention relates to the production of vinyl esters of carboxylic acids.

Vinyl esters of aliphatic carboxylic acids of low molecular weight may be prepared by various known methods from acetylene and the corresponding carboxylic acids under the influence of catalysts; In addition to mercury compounds, which are mainly recommended as catalysts for this purpose, the literature also describes compounds of magnesium, iron, copper, aluminium, tin, boron and iodine as catalysts for working in the liquid phase and under increased pressure. Furthermore, for the preparation of vinyl esters, in particular vinyl acetate, in the gaseous phase, it has already been proposed to lead a mixture of carboxylic acid vapour and acetylene over heated 1 catalysts, inter alia compounds of zinc or cadmium. I

All the said processes only allow of the prepathe fatty acid series. With propionic and butyric acids they give yields which are scarcely of any industrial value while with valeric acid and still higher fatty acids they are a complete failure. Thus it has been impossible hitherto to prepare vinyl esters of fatty acids having more than four carbon atoms in the molecule, so that these esters have hitherto remained unknown.

I have now found that contrary to expectation the vinyl esters of carboxylic acids containing at least 5 carbon atoms in the molecule, 1. e. of aliphatic, saturated and unsaturated, monoand polycarboxylic acids containing at least 5 carbon atoms in the molecule, of cyclic, that is aromatic, cycloaliphatic and heterocyclic, monoand polycarboxylic acids and of mixed aliphatic-aromatic and mixed aliphatic-cycloaliphatic, monoand polycarboxylic acids, the carboxylic groups of which mixed acids may be fixed to the aliphatic as well as to the cyclic residue, may readily be obtained in good yields from acetylene and the corresponding carboxylic acids by employing zinc or cadmium salts of organic carboxylic acids, preferably of the acids used for esterification, as catalysts and by working in the liquid phase, preferably at a pressure above atmospheric pressure.

Suitable aliphatic carboxylic acids are for example normal valeric acid and its isomers, caprylic acid, lauric acid, palmitic acid, margaric acid,

'stearic acid, oleic acid, adipic acid, myristic and mixed aliphatic-aromatic acids, as for example phenyl acetic acid, cinnamic acid, phenylglycine, and polybasic cyclic acids or their acid esters, such as phthalic acid and phthalic acid monoalkyl esters, for example monoethyl, normal or isobutyl esters, cyclic hydroxy-carboxylic acids, as for example salicyclic acid or hydroxynaphthoio acid, and heterocyclic acids, such as pyridine and quinoline carboxylic acids, and hydroaromatic carboxylic acids, as for example hydrophthalic acid. Instead of pure acids, partially esterified acids or resins showing a high acid value, such as colophony, or mixtures of acids may be employed, as for example the mixtures of acids obtainable by the saponification of natural fats and fatty oils containing esters and/or fatty acids, or the mixtures of acids obtainable by oxidizing paraffin wax or Montan wax.

Suitable zin'c and/or cadmium salts of organic acids are'for example zinc acetate, zinc stearate, zinc benzoate or cadmium benzoate. The salts may be added as such to the acid to be treated with acetylene or they may be prepared by dissolving the oxides of zinc or cadmium in the acids to be employed. Generally speaking, the reaction proceeds better and more rapidly with zinc catalysts.

In the preparation of the monomeric esters it is preferable not to employ less than 0.5 per cent of catalysts (calculated as ZnO or CdO with reference to the acid employed) since otherwise the reaction proceeds very slowly and consequently a polymerization of a part of the vinyl ester formed may take place. Generally, the quantity of the catalyst (calculated as stated above) is between about 0.5 and about 5, preferably bein the trade as active carbon, fullers earth or silica gel, may be added to the reaction mixture. Such additions are, however, not necessary since the reaction proceeds quite quickly without any addition of this kind.

. During the reaction the zinc salt probably first reacts with acetylene with the formation of the zinc derivatives of the corresponding vinyl ester. Thisthen reacts with the excess of carboxylic acid with the formation of the free vinyl ester and the the fatty acids the course of the reaction thus corresponds to the following equation:

able to use a pressure-tight reaction tower capable of being heated and if desired, cooled, which is filled with acid in which, say, about 2 per cent of ZnO are dissolved and which is heated to the re- RCOOCH=CH (in which RCOOdenotes the radicle of an aliphatic carboxylic acid containing more than 4 carbon atoms).

Contrary to expectation, no appreciable amounts of ethylidene di-esters are formed although the vinyl esters formed are not removed from the reaction mixture and thus remain in intimate contact with free acids until the end of the reaction. The yield in vinyl esters is usually between about and per cent, calculated on the carboxylic acid employed, about 5 or 10 per cent thereof remainingin the free state until the end of the reaction.

The reaction generally takes place at temperatures between about and about 300 C., temperatures between about and about 190 C. being especially favourable for obtaining good yields. When the boiling point of the acid allows the reaction may be carried out without the employment of pressure, but in almost all cases it is preferable to work in a closed vessel at a pressure above atmospheric pressure, such as between about 5 and about 30 atmospheres, preferably between about 10 and about 20 atmospheres, higher pressures, such as 40, 50, 100 or 200 atmospheres, or still higher pressures being also suitable, provided the pressure and temperature employed be outside the explosionrange of acetylene; by the employment of a superatmospheric pressure the speed of reaction is considerably increased and loss by reason of the polymerization of the vinyl esters is avoided. It is necessary, however, in this case to dilute the acetylene sufficiently with inert gases, such as nitrogen, hydrogen, carbon monoxide, methane, or ethane, in order to preclude explosions. A mixture of 2 volumes of acetylene with 1 volume of nitrogen hydrogen or another of the aforesaid gaseous diluents is usually employed. The danger of explosions may be still further precluded by the addition of inert solvents, as for example aliphatic, aromatic or hydroaromatic hydrocarbons, such as benzine, benzene, toluene, xylene, cyclohexane or decahydronaphthalene, or esters, such as the vinyl esters obtainable according to the present process or such esters as methyl, ethyl, n-butyl, isobutyl, or amyl acetate or butyrate. Forthe sake of brevity the said inert gases and inert solvents will be defined in the following and in the claims as inert diluents. Theemployment of solvents offers an efi'ective protection against polymerization of the vinyl esters at the high reaction temperature and renders possible, especially in the case of employing benzine fractions or other hydrocarbons, a ready and practically quantitative separation of the salts employed as catalysts, the said salts being deposited practically quantitatively under these conditions after cooling the reaction mixture at the end of the reaction and being capable of ready separation from the reaction mixture by filtration.

The process may be carried out discontinuously or continuously. In the latter case it is prefernooo action temperature, acetylene, if desired, diluted with inert gases, being led through the tower from the bottom to the top. The unconverted acetylene is returned to the tower. The vinyl ester formed is continually withdrawn from the upper end of the tower while at the same time fresh acid together with catalyst is introduced at the lower end of the tower.

The distillation of the vinyl esters obtained may also be carried out continuously, whereby, in order to prevent polymerization, the distillation is preferably carried out in vacuo, such as at a pressure between, say, about 2 and about 5 millimeters mercury, while employing enamelled or copper distillation vessels. Vinyl esters of valeric or caproic acids and of like acids of comparatively low molecular weight may, however, be distilled at normal pressure without any risk. Polymerization inhibitors, such as hydroquinone, naphthols or amines, may also be added during the distillation or during the subsequent storage of the vinyl esters. The said polymerization-preventing substances may also be incorporated with the reaction mixture during the reaction itself.

The vinyl esters obtained according to this invention may be polymerized by the usual methods.

The following examples will further illustrate how this invention may be carried out in practice but the invention is not restricted to these examples. The parts are by weight.

Example 5.8 parts of zinc oxide are dissolved in 290 parts of normal valeric acid. The solution is diluted with 290 parts of toluene and treated with a mixture of 2 parts of acetylene and 1 part of nitrogen at 180 C. under a pressure of from 20 to 25 atmospheres in an enamelled stirring autoclave. ,Further acetylene is supplied at the rate at which it is used up. When absorption of acetylene no longer takes place, which is the case after about 20 hours, the reaction mixture is allowed to cool, the deposited zinc valerate is filtered off and the filtrate is subjected to fractional distillation. After separating off the toluene, valeric vinyl ester boiling at about 134 C. at atmospheric pressure, is obtained in a yield of from 70 to 80 per cent of the theoreticalyield.

When employing the equivalent amount of caproic acid instead of valeric acid, caproic vinyl ester (boiling point from about to about 167 C, at atmospheric pressure) is obtained in a similar yield.

In the same manner, caprylic vinylester (boiling point at 12 millimeters of mercury 94 C.) may be obtained from caprylic acid, lauric vinyl ester (boiling point at 4 millimeters of mercury 123 C.) from lauric acid and myristic vinyl ester (boiling point at 3 millimeters of mercury 150 C.) from myristic acid, generally in a yield of about 90 per cent of the theoretical yield. If a mixture of fatty acids, having an average number of carbon atoms between 8 and 12, obtainable by the liquid phase oxidation of paraffin wax by means of oxygen containing gases be employed instead of the aforesaid valeric acid, a mixture of vinyl esters is obtained which boils between about 70 and about 160 C. at 2 millimeters mercury gauge.

Ezcample 2 1000 parts of palmitic acid, in which 20 parts of zinc oxide have been dissolved are freed by heating in vacuo from the water formed during the formation of the zinc palmitate and then heated-in a stirring autoclave with a mixture of acetylene and nitrogen (2:1) to 160 C. under a pressure of from 15 to 20 atmospheres while pressing in acetylene at the rate at which it is used up, until-after about 5 hours-the absorption of acetylene ceases. The reaction product is dissolved while hot in half its weight of benzine (boling point from 100' to 200 C.). After cooling, the zinc 'palmitate is filtered off. By fractional distillation of the filtrate, palmitic vinyl ester (boiling point at 2 millimeters of mercury 165 C.) is obtained in a yield of from to per cent of the theoretical yield.

The zinc palmitate separated by filtration may be employed as the catalyst for a further batch. An equally good result is obtained by using the equivalent amount of zinc acetate instead of zinc oxide.

In a similar manner stearic vinyl ester (boiling point at 2 millimeters of mercury 167 C.) may be obtained in an almost quantitative yield from stearic acid.

(The yields given are with reference to the conversion of fatty acid. This usually amounts to about 90 per cent. The remainder of the fatty acid is recovered unchanged and may be again subjected to the action of acetylene.)

Example 3 1000 parts of oleic acid in which 20 parts of zinc oxide have been dissolved are freed from the water formed during the formation of zinc oleate and then treated in a stirring autoclave with a mixture of acetylene and nitrogen (2:1) at C. as described in Example 2. The theoretical amount of acetylene is absorbed after treatment for about four hours. After cooling, the zinc oleate deposited is filtered off. By fractional distillation of the filtrate oleic vinyl ester (boiling point at 2 millimeters of mercury 173 C.) is obtained in a yield of more than 90 per cent of the theoretical yield.

Example 4 10 parts of zinc oxide are added to 500 parts of commercial linoleic acid, 1. e. a mixture of about 10 per cent of saturated fatty acids (myristic, pahnitic, stearic and arachic acids), about 15 to 20 per cent of oleic acid, from 25 to 35 per cent of linoleic acid and from 35 to 45 per cent of linolenic acid and then dehydrated by heating in vacuo. The solution is diluted with an equal amount of benzine (boiling point from 100 to 200 C.) and treated with a mixture of acetylene and nitrogen as described inExample 3 except that the temperature used is 180 C. The absorption of acetylene is completed after about three hours. After cooling the reaction mixture, the deposited zinc salt is filtered off and the filtrate subjected to distillation in vacuo. About 400 parts of the vinyl esters of a mixture of saturated and unsaturated fatty acids are obtained,

the boiling point at 6 millimeters of mercury being from to 200 C.

Example 5 6 parts of cadmium oxide are introduced into 300 parts of fused benzoic acid, the whole being warmed until dissolution is complete. 500 parts of toluene are then added and the mixture is introduced into an autoclave provided with a stirrer. A quantity of nitrogen corresponding to a pressure of 5 atmospheres and a quantity of acetylene corresponding to a pressure of 10 atmospheres are then pressed in, the stirrer is set in motion, the reaction mixture is heated to from to C. and additional acetylene is pressed in at the rate at which it is consumed. After about 8 hours the amount of acetylene necessary for the formation of the benzoic acid vinyl ester has been consumed. After cooling, the reaction mixture is filtered and distilled in vacuo. Benzoic acid vinyl ester, boiling at from 72 to 74 C.

gauge) and from beta-naphthoic acid the corresponding beta-naphthoic acid vinyl ester having a boiling point of 153 C. at 4 millimeters (mercury gauge). By employing the cadmium or zinc salts of other organic carboxylic acids, as for example of acetic acid, butyric acid, oleic acid or stearic acid, instead of .the zinc or cadmium salts of the cyclic carboxylic acids employed for the esteriflcation, the vinyl esters are obtained in similar good yields Example 6 15 parts of zinc oxide are dissolved in 500 parts of phthalic acid mono-ethyl ester while warming. The solution is fed into a stirring autoclave, a quantity of nitrogen corresponding to an increase in pressure of 5 atmospheres and a quantity of acetylene corresponding to an increase in pressure of 10 atmospheres are introduced, the stirring device is set in motion and the mixture is heated to from 180 to 185 C. The pressure is kept constant by replenishing the acetylene consumed. After several hours the consumption of acetylene ceases and phthalic acid mono-ethyl mono-vinyl ester is formed. The ester may be purified with animal charcoal either as such or after dissolution in benzine.

If instead of the aforesaid phthalic acid monoethyl ester, the same quantity of acetyl salicyclic acid be employed, the vinyl ester of acetyl salicylic acid, boiling between about 145 and about 150 C., at 3 millimeters mercury gauge is obtained.

Example 7 A mixture of 250 parts of anhydrous abietic acid with 10 parts of anhydrous .zinc acetate and 200 parts of anhydrous toluene is introduced into an autoclave provided with a stirrer. The air contained in the autoclave is pressed out by means of nitrogen and then a quantity of nitrogen corresponding to a pressure of 5 atmospheres and a quantity of acetylene corresponding to a pressure of 10 atmospheres are pressed in. The stirrer is set in motion and the reaction mixture is heated to 180 C., and additional acetylene is pressed in at the rate at which it is consumed. .-'After about 12 hours the amount necessary for the formation of the vinyl ester of abietic acid has been consumed. After cooling, the reaction mixture is filtered and distilled in vacuo. At first, the solvent distiis oil and, at a pressure of from 6 to' 7 millimeters mercury gauge, the vinyl ester of abietic acid, boiling between about 200 and 225 C. is obtained. The said ester is athick liquid, thin layers of which are practically colourless, whereas thick layers look slightly yellow.-

Instead of abietic acid the same quantity of a colophony, showing a high acid'value, may be employed with the same result.

The vinyl ester of abietic acid may also be prepared in a similar manner in the absence of any solvent.

What I claim is:

1. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction with a carboxylic acid containing at least carbon atoms, in the liquid phase and with a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium.

2. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction at a pressure above atmospheric pressure, but outside the explosion range of acetylene, with a carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium.

3. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction with a carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with a catalyst selected from the class consisting of salts of zinc and cadmium with the carboxylic acid employed as initial material.

4. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction with a carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with at least 0.5 per cent, oi the weight oi said carboxylic acids, of a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium, calculated as zinc and cadmium oxides.

5. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction with a carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with at least 0.5 per cent of the weight of said carboxylic acid of a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium, calculated as zinc and cadmium oxides, in the presence of a solid, adsorptive substance.

6. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction at a pressure above atmospheric pressure with a carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium in the presence of an inert diluent.

7. In the catalytic production of vinyl esters by the action of acetylene on carboxylic acids, the step which comprises carrying out the reaction with an aliphatic carboxylic acid containing at least 5 carbon atoms, in the liquid phase and with a catalyst selected from the class consisting of carboxylic acid salts of zinc and cadmium.

8. In the catalytic production of vinyl esters by the action oi acetylene on carboxylic acids,

' containing at least 8 carbon atoms.

10. The vinyl ester of lauric acid. 11. The vinyl ester 01 stearic acid.

WALTER REPPE. 

